The present invention relates to a device for connecting and disconnecting a dampening system and an ink supply system in an offset printing machine.
Generally, as shown in FIGS. 1(a) and 1(b) of the accompanying drawings, an offset printing machine includes an ink supply system or inking system A operatively coupled to a drive source (not shown) of the printing machine and a dampening medium supply system or dampening system B operatively coupled to the drive source or drivable by an independent motor (not shown). Ink and a dampening medium are supplied by the inking system A and the dampening system B, respectively, to and coated On a master plate (not shown) disposed over a plate cylinder 7. The mixture of the ink and the dampening medium is then transferred onto a blanket cylinder 6, so that an image corresponding to an image of the original master plate is transferred onto the blanket cylinder 6. Then the inked image on the blanket cylinder 6 is transferred onto a printing sheet 1 of paper fed between the blanket cylinder 6 and an impression cylinder 8 by a sheet feed mechanism 2. The printed sheet 1 is then discharged onto a sheet table 4 by a sheet discharge mechanism 3.
As shown in FIGS. 1(a) and 1(b), the inking system A includes an ink fountain roller 11 and ink applicator rollers 5, 10, and further includes, between the fountain roller 11 and the ink applicator rollers 5, 10, an ink ductor roller 12, an ink fast roller 13, a first ink delivery roller 14, an ink delivery transfer roller 17, a second ink delivery roller 18, a third ink delivery roller 19, and an ink transfer roller 20.
Further, as shown in FIGS. 1(a) and 1(b), the dampening system B includes a dipping roller 22 and an applicator roller 9, and further includes, between these rollers 22 and 9, a dampening medium tank 21, a metering roller 24, a dampening medium distributor or ductor roller 23 (23') and a transfer roller 16. The contact pressure between the metering roller 24 and the fountain roller 22 is variable to control the amount of water supplied to the applicator rollers in the device shown in FIG. 1(a). On the other hand, in the conventional device shown in FIG. 1(b), the dampening medium ductor roller 23' is movable between the fountain roller 22 and the transfer roller 16 to control the amount of water supplied to the applicator rollers.
In order for the printing machine to produce good prints, it is necessary that ink be continuously and smoothly supplied to the dampening system B by the inking system A, or the dampening medium be continuously and smoothly supplied to the inking system A by the dampening system B, or the dampening medium and ink be continuously and smoothly supplied between the inking and dampening systems A and B, dependent on the types of the ink and printing sheets or the area of an image to be printed.
In this connection, in the conventional devices shown in FIGS. 1(a) and 1(b), an intermediate roller 15 is provided which is movable between the inking and dampening systems A and B, i.e., between the third ink delivery rollers 19 and the dampening medium transfer roller 16.
FIG. 2 shows still another conventional device which particularly concerns a device for connecting and disconnecting a dampening system B' and an ink supply system A' in an offset printing machine which is designed to meet the above requirements. The device shown in FIG. 2 has an ink distributor roller or an intermediate roller 15a disposed between a dampening medium applicator roller 9 and an ink applicator roller 10. As described above, the roller 9 is held against an original plate on a plate cylinder 7 for applying a dampening medium to the original plate, and the ink applicator rollers 5, 10 are adapted for applying ink to the original plate. The distributor or the intermediate roller 15a is movable between the applicator rollers 9 and 10 for connecting and disconnecting the dampening system B' and inking system A'. The intermediate roller 15a is rotatably supported on a bracket b on which the ink applicator roller 10 is also supported. The bracket b is pivotally supported to a shaft 20a of an ink transfer roller 20, so that the ink applicator roller 10 can be moved toward and away from the master plate disposed over the plate cylinder 7. This conventional structure is described in Japanese Patent Application Kokai No. 55-57464.
In the conventional arrangement shown in FIG. 2, since the distributor roller 15a as well as the ink applicator roller 10 are supported on the identical bracket b, when the ink applicator roller 10 is held against the plate cylinder 7, the intermediate roller 15a is also held against the water applicator roller 9. Therefore, according to the conventional arrangement, the dampening system B' and ink supply system A' cannot be separated from each other, when the ink applicator roller 10 is in contact with the plate cylinder 7. Conversely, when the dampening system B' and ink supply system A' are separated from each other, the ink applicator roller 10 cannot be brought into contact with the plate cylinder 7. Another problem is that the entire device is complex in structure. U.S. Pat. No. 4,351,236 discloses a combined dampening and inking unit similar to the device described above.